Question

The gas in a refrigerator causes cooling on expansion because:
(a) The density of gas goes down
(b) Heat of the gas is lost as work is done by the gas
(c) Work done by the gas is converted into he

Answer 1

Imagine the gas was in a cylinder and expanded by pushing against a piston. The movement would involve work being done. This work would need energy, which would come from the kinetic energy of the gas molecules hitting the piston- reducing their average speed. Taking KE away corresponds to lowering the temperature of the gas.
(b) Heat of the gas is lost as work is done by the gas.